The legal complaint alleges that Ofcom uses its powers under the Online Safety Act to threaten to impose "ruinous civil penalties and referrals to law enforcement for criminal penalties, including arrest and imprisonment" to American citizens and businesses if its orders are not obeyed.
It seeks to "restrain Ofcom's conduct and its continuing egregious violations of Americans' civil rights, including, without limitation, to the right of freedom of speech".
Ronald Coleman of the Coleman Law Firm, which is also acting for the plaintiffs 4chan and Kiwi Farms, said his clients were defending "the free speech rights of every American."
"We have asked the Court to confirm that Ofcom has no authority to impose or enforce unconstitutional UK laws on American soil."
Among the actions the legal case seeks the court to take are:
A declaration that Ofcom's orders and demands are unenforceable in the US as they are inconsistent with the First, Fourth, and Fifth Amendments to the US Constitution, relevant US legislation and public policy.
A permanent injunction prohibiting Ofcom from enforcing or attempting to enforce the Online Safety Act against the plaintiffs in the US.